mcpwm_capture_channel_enable() function

- ESP_OK: Enable MCPWM capture channel successfully - ESP_ERR_INVALID_ARG: Enable MCPWM capture channel failed because of invalid argument - ESP_ERR_INVALID_STATE: Enable MCPWM capture channel failed because the channel is already enabled - ESP_FAIL: Enable MCPWM capture channel failed because of other error

This function will transit the channel state from init to enable. This function will enable the interrupt service, if it's lazy installed in `mcpwm_capture_channel_register_event_callbacks()`.